She was living happily in Battersea with her four-year-old son Eduardo until she was forced to leave in April 2011 after her landlord refused to renew her tenancy.

Sandra is now homeless, and cannot find affordable accommodation in her area because of the housing benefit cap.

Wandsworth Council has a duty to house Sandra as a homeless person. In most cases the current process results in an offer of social housing, often after a long spell in temporary accommodation. But due to changes under the Localism Act, which will soon come into force, that process will change dramatically, say housing charities.

Under the new legislation homeless people would have to accept an offer of 12 months of private accommodation - which could well be outside the borough - or be forced to make arrangements on their own.

Charities are now arguing that government regulations for assessing whether accommodation offered for a 12-month tenancy is "suitable" should include basic provisions to ensure families are not forced to move too far if, for instance, a child is in the middle of GCSE exams.

Unless that is set out in the regulations, charities told the Huffington Post UK, councils will more often look to move families further outside the borough, and those affected will not be able to seek redress though the courts.

The chief executive of housing charity Shelter, Campbell Robb, said on Tuesday: "This is the terrifying reality of our housing crisis today - hundreds of families potentially forced to move halfway across the country, uprooted from schools, support networks and employment opportunities.

"Most worryingly, this is only the thin end of the wedge, as further reductions in the housing safety net start to bite over the coming months.

"The dangerous cocktail of cuts to housing benefit and spiralling rents is making finding a decent home increasingly unaffordable for families across the country. Those unable or unwilling to move away from their local area may be forced to overcrowd or accept a home in appalling conditions to make ends meet."

Wandsworth Council told the Huffington Post UK that while 90% of its homeless households were eventually relocated within the borough, the other 10% were relocated elsewhere in Greater London.

Several other London councils said they had relocated residents outside local areas.

Houslow Council said that it is "normal practice" for a borough of its type, although it said only "a very small number of households [had been moved to] neighbouring boroughs".

"This is only done after careful consideration of their needs, such as family arrangements and support networks," a spokesperson said.

Hackney Council said it was increasingly being forced to look afield. It said in a statement: "Hackney Council is continuing to make use of suitable homes in Hackney and neighbouring boroughs to meet housing needs, however this is becoming increasingly difficult to sustain due to the recent changes to Housing Benefit."

Waltham Forest Council said it had moved families outside London, including a dozen households who were relocated to Luton in 2010. Properties in Kent, High Wycombe and other locations are also being considered for future relocations.

Tower Hamlets Council said it understood "the importance of keeping families in their local communities" but added that moving them elsewhere may "become an option" if it is "forced to consider to avoid families falling into rent arrears or becoming overcrowded to meet rent costs".

Additionally, Southwark Council said 10 claimants had already been affected by the benefit cap, but said it was "early days" and would only move tenants out of the borough as a "last resort".

Prime minister David Cameron's official spokesman told the Press Association: "We are making some reforms to the benefit system. Even after the reforms come through, people will still be able to claim nearly £21,000 a year to cover their rent through housing benefit.

"We think tenants on housing benefit should have to make the same choices as other tenants have to make ... Yes, we are reforming housing benefit. Yes, those changes will mean some people have to move."

Additional reporting by Asa Bennet and Charlie Lindlar.

CORRECTION: An earlier version of this story reported that some Wandsworth tenants had been relocated outside Greater London, which is not accurate. Wandsworth Council said 90% of its homeless households were relocated in Wandsworth, and the other 10% were relocated within Greater London.